Incompatible Change:
When auto_increment_increment is greater than
one, values generated by a bulk insert that reaches the maximum
column value could wrap around rather producing an overflow
error.

As a consequence of the fix, it is no longer possible for an
auto-generated value to be equal to the maximum BIGINT
UNSIGNED value. It is still possible to store that
value manually, if the column can accept it.
(Bug #39828, Bug #11749800)

Important Change; Partitioning:
Date and time functions used as partitioning functions now have
the types of their operands checked; use of a value of the wrong
type is now disallowed in such cases. In addition,
EXTRACT(WEEK FROM
col_name), where
col_name is a
DATE or
DATETIME column, is now
disallowed altogether because its return value depends on the
value of the
default_week_format system
variable.
(Bug #54483, Bug #11761948)

References: See also Bug #57071, Bug #11764255.

InnoDB:
The InnoDB system tablespace could grow
continually for a server under heavy load.
(Bug #57611)

InnoDB:
If the server crashed during an ALTER
TABLE operation on an InnoDB table,
examining the table through SHOW CREATE TABLE
or querying the INFORMATION_SCHEMA tables
could cause the server to stop with an assertion error.
(Bug #56982)